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Thursday, October 7, 2010

Peridot - Part 1: Gem of the Earth's Interior

Greetings Gemstone Fans:

I thought I'd open up my blogging about beading materials with a series of posts on the gemstone peridot. This is the lovely green stone commonly known as August's birthstone. In gem-quality, it is peridot, but the mineral is known to geologists as olivine. The basic part of its structure is created by silicon and oxygen, as with most other 'rocky' minerals on Earth. Olivine also contains varying amounts of magnesium and iron.

We imagine that a gemstone held as precious by humans must be quite an oddity - something very rare. Yet olivine in its many forms is one of the most abundant minerals making up the planet Earth.

In fact, olivine accounts for the bulk of the Earth's upper mantle. The mantle is that thick, voluminous layer that sits between the Earth's thin crust and its core of iron and nickel. In this image, the mantle is (appropriately) green, with the upper mantle labeled as region three.

Because of the important role olivine plays in the Earth's composition, and its place in the upper mantle, geologists spend a great deal of time trying to understand how the mineral behaves at different pressures and temperatures, and which forms are created when and where. This information is needed to properly model heat flow, as well as the movement of the continental plates. So this stone is not only of interest to gem fans, it is a critical piece of Earth's geologic puzzle.

When you touch peridot, it is like touching the inside of the planet. Or possibly literally touching it, since some peridot is brought up to the surface from the depths by volcanism.

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